A common problem with feed wheels for tree trunks is that bark and wood material from the trunks collects and becomes fixed to the periphery of the wheel in the spaces between the rows of drive teeth. The normally means that the depth of penetration of the drive teeth is reduced, such that the feed wheels acquire a poorer feed capacity, and this in turn means that the contact pressure of the feed wheels must be increased, leading to the wheels and tree trunks being subject to greater wear and damage. The accumulation of this material on the periphery of the rollers also causes their effective rolling diameter to vary in an unpredictable manner. If they are then used for the measurement of timber from processed tree trunks, as is common in, for example, single-grip harvesters, unreliable measurement results are obtained. It is thus strongly desired to prevent the accumulation of bark and wood material on the feed wheels.
Many attempts have been previously made to solve this problem. The teeth in one known type of feed wheel have such a large height that the accumulation of a certain amount of material on the wheels is permitted, and the self-cleaning properties of the tops of the teeth are relied on, in that the outermost layer of foreign material is relatively easily torn off from an underlying material layer. Such high teeth, however, can cause damage to the tree trunks. It is also known to make the supports spring-loaded against springs of, for example, a rubber material at the peripheral surface of the wheel, whereby the spring movements of the supports have a certain self-clearing influence on the collected bark and wood material. Such wheels, however, have relatively high maintenance costs due to the fact that the springs have a limited lifetime. The bases of the teeth in a further type of feed wheel are arranged elevated onto a plateau of the support above the periphery of the feed wheel. The plateau can be considered to be similar to a protective ring—such as that on a ski pole—that partially prevents the teeth sinking too deeply into the softer bark material, and in this way partially prevents the material falling down into the spaces between the supports.